It is known that some types of cellulose pulp made from wood have a high resin content, e.g. various types of mechanical pulp and pulp made by a sulphite process.
Mechanical pulping, alone or combined with a gentle chemical treatment, is widely used in the manufacture of pulps. Thus, chemithermomechanical pulps (CTMP) are produced by refining chemically pre-treated chips with yields of 85-95%. This chemical pre-treatment normally comprises impregnating the chips with an alkaline sulphite solution. The chips, thus impregnated with chemicals, are heated to temperatures above 100.degree. C. and thereafter refined under pressure. The pulp is then normally screened and bleached. Bleaching is most often effected with hydrogen peroxide in an alkaline environment. One use for CTMP is found in the manufacture of sanitary articles, such as disposable diapers and similar absorption products. The processes used for producing mechanical pulp (such as CTMP) occur at pH in the range 4-9, and the components of the wood undergo relatively small chemical changes; the pulp therefore has a considerable content of resin.
The resin can create disturbances in the process of pulp manufacture and may also have a negative effect on the properties of the final pulp product. The ability of fluff-pulp to absorb aqueous liquids is of particular importance. The rate at which absorption takes place is also of particular significance. Since fat has a water-repelling nature, a high fat content will have a negative effect on the absorption rate. Further, agglomerated resin may cause paper breakage during paper manufacture or during printing.
Resin of wood material is soluble in organic solvents and, to a large extent, is comprised of hydrophobic components. It is known that the hydrophobic part of resin contains considerable amounts of triglycerides, more commonly known as fats, and other esters. The triglycerides play a large part in rendering the resin hydrophobic, therewith making it less possible to wash the resin from the pulp. It would be desirable to hydrolyse these as the hydrolysis products are more easily removed in aqueous systems.
Triglyceride hydrolysis can be achieved by treating the wood with a strongly alkaline liquid, similar to what takes place during sulphate cooking. Such alkaline conditions cannot be permitted in the manufacture of CTMP-pulp, however, because of discoloration, reduction in yield, etc. CTMP pulp therefore has a considerable content of triglycerides and esters from resin. It would be beneficial to find a catalyst other than alkali for the triglyceride hydrolysis process.
A low fat content can be obtained to some extent, by storing chips or roundwood. Thus, GB 1,189,604 and U.S. Pat. No 3,486,969 disclose a process for removing resin constituents from wood chips by applying microorganisms to wood chips during storage. This process, however, takes a relatively long time to carry out (at least one month) and is difficult to control, as temperature, residence time, microbial flora etc. may fluctuate. Furthermore, the storage of chips results in discoloration (darkening), and the microorganisms may secrete cellulase and hemicellulase that decreases fibre strength and yield.
The hydrolysis of wood-fat (triglycerides) during storage has been ascribed to fat-hydrolysing enzymes, i.e. lipases. (Anders Assarsson: "Hartsets forandring under vedlagring", Svensk Papperstidning published -72, pages 304-311).
It is an object of the invention to provide a controllable process for hydrolysing resin in pulp to form free acids which can be readily washed from the pulp. It is also an object to provide fluff-pulp having improved liquid absorbency, produced by such a process.